We investigate the use of "photonic lanterns" as adiabatic mode converters for space-division multiplexing (SDM) systems to interface multiple single-mode fibers to a multi-mode fiber. In a SDM ...system, minimizing the coupling loss and mode-dependent loss best utilizes all spatial modes of the fiber which increases the capacity, the transmission distance, and minimizes the outage probability. We use modal analysis, the beam propagation method, and a transfer matrix technique to analyze the lanterns throughput along with its mode dependent loss and show that unitary coupling between single-mode fibers and a multi-mode fiber is only possible by optimizing the arrangements of the cores. Results include simulations for three, 12, 15, and 51 core lanterns to couple to six, 24, 30, and 102 spatial and polarization modes, respectively.
The "photonic lantern," an optical fibre device that has emerged from the field of astrophotonics, allows for a single-mode photonic function to take place within a multimode fibre. We study and ...evaluate the modal behaviour of photonic lanterns as well as the conditions for achieving low-loss between a multimode fibre and a "near-diffraction limited" single-mode system. We also present an intuitive analogy of the modal electromagnetic propagation behaviour along the photonic lantern transition in terms of the Kronig-Penney model in Quantum Mechanics.
Fiber Bragg gratings (FBGs) have proven to be an effective and efficient solution for suppressing OH lines in near-infrared astronomical spectroscopy. Previous studies have focused on designing and ...fabricating FBGs for astronomy H band (1.45-1.7 microns), but the OH lines in J band (1.1-1.4 microns) remain unresolved. In this study, we present a full step-by-step design process for FBGs used for OH suppression in astronomical spectroscopy for the first time. This process includes an improved removal method for OH doublets, optimization techniques, and compensation for visibility degradation. We also demonstrate the success of this process by presenting the first ever fabricated FBGs for use in the J band. Our results show that the capability to design and fabricate FBG filters for any wavelength range within the J and H bands has been achieved.
Abstract
Adaptive optics (AO) is critical in astronomy, optical communications and remote sensing to deal with the rapid blurring caused by the Earth’s turbulent atmosphere. But current AO systems ...are limited by their wavefront sensors, which need to be in an optical plane non-common to the science image and are insensitive to certain wavefront-error modes. Here we present a wavefront sensor based on a photonic lantern fibre-mode-converter and deep learning, which can be placed at the same focal plane as the science image, and is optimal for single-mode fibre injection. By measuring the intensities of an array of single-mode outputs, both phase and amplitude information on the incident wavefront can be reconstructed. We demonstrate the concept with simulations and an experimental realisation wherein Zernike wavefront errors are recovered from focal-plane measurements to a precision of 5.1 × 10
−3
π
radians root-mean-squared-error.
Since its emergence two decades ago, astrophotonics has found broad application in scientific instruments at many institutions worldwide. The case for astrophotonics becomes more compelling as ...telescopes push for AO-assisted, diffraction-limited performance, a mode of observing that is central to the next-generation of extremely large telescopes (ELTs). Even AO systems are beginning to incorporate advanced photonic principles as the community pushes for higher performance and more complex guide-star configurations. Photonic instruments like Gravity on the Very Large Telescope achieve milliarcsec resolution at 2000 nm which would be very difficult to achieve with conventional optics. While space photonics is not reviewed here, we foresee that remote sensing platforms will become a major beneficiary of astrophotonic components in the years ahead. The field has 'given back' with the development of new technologies (e.g. photonic lantern, large area multi-core fibres) already finding widespread use in other fields; Google Scholar lists more than 400 research papers making reference to this technology. This short review covers representative key developments since the 2009 Focus issue on Astrophotonics.
We demonstrate single mode terahertz (THz) guidance in hollow-core kagome microstructured fibers over a broad frequency bandwidth. The fibers are characterized using a THz time-domain spectroscopy ...(THz-TDS) setup, incorporating specially designed THz lenses to achieve good mode overlap with the fundamental mode field distribution. Losses 20 times lower than the losses of the fiber material are observed in the experiments, as well as broad frequency ranges of low dispersion, characteristic of hollow-core fibers.
We present a new technique allowing the fabrication of large modal count photonic lanterns for space-division multiplexing applications. We demonstrate mode-selective photonic lanterns supporting 10 ...and 15 spatial channels by using graded-index fibres and microstructured templates. These templates are a versatile approach to position the graded-index fibres in the required geometry for efficient mode sampling and conversion. Thus, providing an effective scalable method for large number of spatial modes in a repeatable manner. Further, we demonstrate the efficiency and functionality of our photonic lanterns for optical communications. Our results show low insertion and mode dependent losses, as well as enhanced mode selectivity when spliced to few mode transmission fibres. These photonic lantern mode multiplexers are an enabling technology for future ultra-high capacity optical transmission systems.
We demonstrate the first all-fiber mode-group-selective photonic lantern using multimode graded-index fibers. Mode selectivity for mode groups LP(01), LP(11) and LP(21)+LP(02) is 20-dB, 10-dB and ...7-dB respectively. The insertion loss when butt coupled to multimode graded-index fiber is below 0.6-dB. The use of the multimode graded-index fibers in the taper can significantly reduce the adiabaticity requirement.
We demonstrate a novel technology that combines the power of the multi-object spectrograph with the spatial multiplex advantage of an integral field spectrograph (IFS). The Sydney-AAO (Australian ...Astronomical Observatory) Multi-object IFS (SAMI) is a prototype wide-field system at the Anglo-Australian Telescope (AAT) that allows 13 imaging fibre bundles ('hexabundles') to be deployed over a 1-degree diameter field of view. Each hexabundle comprises 61 lightly fused multi-mode fibres with reduced cladding and yields a 75 per cent filling factor. Each fibre core diameter subtends 1.6 arcsec on the sky and each hexabundle has a field of view of 15 arcsec diameter. The fibres are fed to the flexible AAOmega double-beam spectrograph, which can be used at a range of spectral resolutions (R=λ/δλ≈ 1700-13 000) over the optical spectrum (3700-9500 Å). We present the first spectroscopic results obtained with SAMI for a sample of galaxies at z≈ 0.05. We discuss the prospects of implementing hexabundles at a much higher multiplex over wider fields of view in order to carry out spatially resolved spectroscopic surveys of 104-105 galaxies.
Optical vortex beams that carry orbital angular momentum (OAM), also known as OAM modes, have attracted considerable interest in recent years as they can comprise an additional degree of freedom for ...a variety of advanced classical and quantum optical applications. While canonical methods of OAM mode generation are effective, a method that can simultaneously generate and multiplex OAM modes with low loss and over broad spectral range is still in great demand. Here, via novel design of an optical fiber device referred to as a photonic lantern, where the radial mode index ("m") is neglected, for the first time we demonstrate the simultaneous generation and multiplexing of OAM modes with low loss and over the broadest spectral range to date (550 nm). We further confirm the potential of this approach to preserve the quality of studied OAM modes by fusion splicing the end-facet of the fabricated device to a delivery ring-core fiber (RCF).
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